Upon pulmonary infection of CF patients, Pseudomonas aeruginosa undergoes mucoid conversion and acquires the ability to cause chronic, debilitating, and life-threatening disease. The mucoid phenotype is due to the overproduction of alginate, a capsule-like exopolysaccharide that confers resistance to phagocytosis and new adherence properties. Adaptive mutations occur in vivo to de-repress an alternative ECF sigma factor, sigma-22, which leads to the overproduction of alginate. Our long term goal is to characterize the complex regulatory pathways that respond to stress and lead to the activation of genes for alginate biosynthesis. A simple bioassay was developed to test for activation of the promoter of the alginate biosynthetic operon, PalgD. We have discovered that exposure of P. aeruginosa to antibiotics that interfere with cell wall synthesis activates PalgD. This response to cell wall stress requires sigma-22 and the two- component regulators, AlgB and AlgR. In addition, the AlgW protease (a homogue of DegS in E. coli) is also required for the activation of PalgD in cell wall stress response. These discoveries provide valuable new tools and important insights into our understanding the mechanism of sigma-22 control of alginate in P. aeruginosa. We will pursue 3 aims directed at understanding the activation of alginate gene expression: 1. Elucidate the mechanism of regulated proteolysis that activates sigma-22 under conditions of cell wall stress. 2. Characterize the stress signals elicited by antibiotics that affect cell wall homeostasis and activate genes for alginate biosynthesis. 3. Define the role of the 2-component regulator, AlgB, in the alginate gene regulon. These studies will greatly improve our understanding of the complex regulatory pathway that induces alginate production in P. aeruginosa and may lead to novel therapeutic approaches.